1. Field of the Invention
The present invention relates to carrageenan compositions, and to methods for producing carrageenan compositions. The present invention further relates to products containing carrageenan compositions.
2. Background of the Invention and Related Information
For a variety of applications there is a need for aqueous gels that have a high degree of temperature sensitivity. For example, in food products there is often a need for a gel which has a gummy texture, a high degree of cohesiveness and displays bounciness at low temperatures of about 5 to 15.degree. C., yet readily melts in the mouth of the consumer at temperatures of about 25 to 37.degree. C. Similarly for applications such as aqueous gel cosmetics and pharmaceutical products for topical application to the skin, it is also desirable to have a gel component that is firm at lower temperatures yet softens at or near human body temperature.
The most popular of these gelling agents is gelatin, a heterogeneous mixture of water-soluble proteins of high average molecular weight. Gelatin does not occur naturally, but is derived from collagen using a hydrolytic process. Gelatin is usually obtained by boiling bovine or swine skin, tendons, ligaments, bones, etc., but may also be obtained from fish skin.
In its gelling qualities, gelatin is unsurpassed. It is superlative in its gel strength, gel strength loss, lack of gumminess, and "ring." However, because it is necessarily derived from animals, it suffers its own unique drawbacks. For example, gelatin is unacceptable to those of Jewish and Muslim faith, as it is usually prepared from swine skin. Additionally, the safety of the use of gelatin in foods has recently been questioned because of the possible link between consumption of foods prepared from bovine renderings and the occurrence of the fatal Creutzfeldt-Jakob disease. Finally, there are those who are ethically opposed to the consumption of animals or animal-derived products.
For the foregoing reasons, there is a desire, and a need, in the marketplace for a plant-derived gelling agent. A variety of such agents exist, but one of the best known is carrageenan, which is found in abundance in seaweed. Carrageenans are polysaccharides, and specifically galactans, comprising alternating copolymers of .alpha.(1.fwdarw.3)-D-galactose and .beta.(1.fwdarw.4)-3,6-anhydro-D-galactose units. Several members of the carrageenan family are known, differing in their amounts of sulfate ester and/or other substituent groups, including iota-carrageenan, kappa-carrageenan and lambda-carrageenan, of which only iota- and kappa-carrageenans have gelling properties.
A general formula for carrageenan is disclosed by NIJENHUIS, K. in Advanced Polymer Science 130, 203-218, (1997) (hereinafter NIJENHUIS), which is hereby expressly incorporated by reference as though set forth in full herein. STORTZ, C. A. and CEREZO, A. S. describe in Carbohydrate Research 145 (1986), 219-235 (hereinafter STORTZ and CEREZO, which is expressly incorporated by reference as though set forth in full herein), the different members of the carrageenan family by their idealized repeating units:
__________________________________________________________________________ Carrageenan 3-linked residue 4-linked residue __________________________________________________________________________ Beta Beta-D-galactopyranose 4- 3,6-anhydro-alpha-D-galactopyranose sulfate Kappa Beta-D-galactopyranose 4- 3,6-anhydro-alpha-D-galactopyranose sulfate Iota Beta-D-galactopyranose 4- 3,6-anhydro-alpha-D-galactopyranose 2- sulfate sulfate Mu Beta-D-galactopyranose 4- Alpha-D-galactopyranose 6-sulfate sulfate Nu Beta-D-galactopyranose 4- Alpha-D-galactopyranose 2,6-disulfate sulfate Lambda Beta-D-galactopyranose 2- Alpha-D-galactopyranose 2,6-disulfate sulfate (70%) and Beta-D- galactopyranose (30%) Theta Beta-D-galactopyranose 2- 3,6-anhydro-alpha-D-galactopyranose 2- sulfate sulfate Xi Beta-D-galactopyranose 2- Alpha-D-galactopyranose 2-sulfate sulfate __________________________________________________________________________
It is generally known that the gelling ability of carrageenan is influenced by alkali treatment, through which a 3,6-anhydro bond is formed via a de-esterification of the C-6 sulfate esters present, thus causing a decrease in water solubility. The viscoelastic behavior of carrageenans is affected not only by alkali treatment, but by electrolyte concentration, carrageenan type, protein interaction, molecular weight and concentration of the carrageenan, as well as temperature. A general discussion of the qualities of carrageenans is presented in Chapter 3 of Thickening and Gellin Agents for Food, Second Edition (Imeson, ed., Chapman & Hall, N.Y. 1997) (hereinafter IMESON), and in Chapter 7 of Industrial Gums: Polysaccharides and Their Derivatives, Third Edition (Whistler and BeMiller, eds., Academic Press, San Diego 1993) (hereinafter WHISTLER). IMESON and WHISTLER are hereby expressly incorporated by reference as though set forth in full herein. Thus, the complex mechanisms underlying the viscoelastic behavior of a particular carrageenan makes it difficult to predict the properties thereof. Moreover, viscoelastic behavior is sometimes not predictive of subjective consumer preference.
Presently, there is room for improvement in commercially available carrageenans. For example, temperature sensitivity of currently available carrageenans is somewhat inadequate, i.e., while the carrageenans may have a desirable elastic texture at temperatures below 15 to 20.degree. C., they are gummy at temperatures prevailing in the mouth. Ideally, the carrageenans should show viscous or plastic characteristics in order to be useful as gelling agents in, for example, water desserts. Furthermore, the present commercially available carrageenans are characterized by forming relatively rigid gel structures, which do not show the desired "ring," which is desirable in some applications, such as water desserts and milk desserts. Additionally, the presently available carrageenans are not completely satisfactory from a subjective consumer point of view.
A number of processes exist for the extraction and modification of carrageenans, each contributing in different ways to the qualities of the finished product. Examples include Ciancia, M. et al. Carbohydrate Polymers 32, (1997), 293-295, "Alkaline modification of carrageenans. Part III. Use of mild alkaline media and high ionic strengths," (hereinafter CIANCIA) in which alkaline modification of carrageenans by the use of sodium carbonate at pH-values of at least 12 is presented. CIANCIA is hereby expressly incorporated by reference as though set forth in full herein.
U.S. Pat. No. 2,624,727, to LEGLOAHEC ("LEGLOAHEC"), is an early example of a method for extracting carrageenan from seaweeds. LEGLOAHEC emphasizes the need for having cations present in the extraction step for cation exchange.
U.S. Pat. No. 3,094,517, to STANLEY ("STANLEY") is directed to a process for extracting carrageenans from seaweed. STANLEY presents an extensive discussion of the role of alkaline hydrolysis in the extraction procedure. Calcium hydroxide is described as preferable for the extraction procedure.
U.S. Pat. No. 3,176,003, to STANICOFF is directed to a process for extracting kappa and lambda carrageenans from seaweed using hydroxide salts.
U.S. Pat. No. 3,342,612, to FOSTER et al. ("FOSTER") discloses extractives derived from sea plants and their recovery and treatment, as well as compositions comprising such extractives including aqueous gels. In particular, FOSTER discloses that an extractive may be obtained from Eucheuma spinosum and Agarchiella tenera and emphasizes that, as compared to conventional processes, the amount of calcium hydroxide is important, as is the temperature. Optimally, the quantity of calcium hydroxide is disclosed to be about 7% by weight, based on the weight of the dry sea plant. The preferred temperature is disclosed to be from about 90.degree.-100.degree. C.
U.S. Pat. No. 3,907,770, to STRONG is directed to a process for extracting carrageenan from seaweed using a process which includes digesting at elevated temperatures a mixture of seaweed with water and an alkaline earth metal hydroxide or an alkali metal hydroxide. The seaweed content is disclosed to be equal to at least about 9% by weight, based on the dry weight of the seaweed.
U.S. Pat. No. 5,502,179, to LARSEN discloses a carrageenan product which is disclosed to be useful as an emulsifier and for thickening or gelling aqueous systems. The product is apparently made by subjecting a carrageenan-containing material in which 6-sulfated galactose units have been converted into 3,6-anhydro galactose units to a shear stress treatment.
In the alkaline extraction of carrageenan from seaweed, nu carrageenan, which is present in the seaweed, is converted to iota carrageenan, which is also present in the seaweed. This conversion is generally seen as desirable when iota carrageenan is the desired end product. This reaction is described in WHISTLER and shown diagrammatically as follows: ##STR1##
However, none of the presently available carrageenans provide the desired combination of elastic characteristics at temperatures below room temperature and plastic and/or viscous characteristics at mouth and body temperatures.